linux-cve-announce - CVE-2025-38059: btrfs: avoid NULL pointer dereference if no valid csum tree

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Message-ID: <2025061834-CVE-2025-38059-4697@gregkh>
Date: Wed, 18 Jun 2025 11:33:54 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38059: btrfs: avoid NULL pointer dereference if no valid csum tree

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

btrfs: avoid NULL pointer dereference if no valid csum tree

[BUG]
When trying read-only scrub on a btrfs with rescue=idatacsums mount
option, it will crash with the following call trace:

  BUG: kernel NULL pointer dereference, address: 0000000000000208
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  CPU: 1 UID: 0 PID: 835 Comm: btrfs Tainted: G           O        6.15.0-rc3-custom+ #236 PREEMPT(full)
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS unknown 02/02/2022
  RIP: 0010:btrfs_lookup_csums_bitmap+0x49/0x480 [btrfs]
  Call Trace:
   <TASK>
   scrub_find_fill_first_stripe+0x35b/0x3d0 [btrfs]
   scrub_simple_mirror+0x175/0x290 [btrfs]
   scrub_stripe+0x5f7/0x6f0 [btrfs]
   scrub_chunk+0x9a/0x150 [btrfs]
   scrub_enumerate_chunks+0x333/0x660 [btrfs]
   btrfs_scrub_dev+0x23e/0x600 [btrfs]
   btrfs_ioctl+0x1dcf/0x2f80 [btrfs]
   __x64_sys_ioctl+0x97/0xc0
   do_syscall_64+0x4f/0x120
   entry_SYSCALL_64_after_hwframe+0x76/0x7e

[CAUSE]
Mount option "rescue=idatacsums" will completely skip loading the csum
tree, so that any data read will not find any data csum thus we will
ignore data checksum verification.

Normally call sites utilizing csum tree will check the fs state flag
NO_DATA_CSUMS bit, but unfortunately scrub does not check that bit at all.

This results in scrub to call btrfs_search_slot() on a NULL pointer
and triggered above crash.

[FIX]
Check both extent and csum tree root before doing any tree search.

The Linux kernel CVE team has assigned CVE-2025-38059 to this issue.


Affected and fixed versions
===========================

	Fixed in 6.6.93 with commit 50d0de59f66cbe6d597481e099bf1c70fd07e0a9
	Fixed in 6.12.31 with commit 6e9770de024964b1017f99ee94f71967bd6edaeb
	Fixed in 6.14.9 with commit d35bed14b0bc95c6845863a3744ecd10b888c830
	Fixed in 6.15 with commit f95d186255b319c48a365d47b69bd997fecb674e

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-38059
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/btrfs/scrub.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/50d0de59f66cbe6d597481e099bf1c70fd07e0a9
	https://git.kernel.org/stable/c/6e9770de024964b1017f99ee94f71967bd6edaeb
	https://git.kernel.org/stable/c/d35bed14b0bc95c6845863a3744ecd10b888c830
	https://git.kernel.org/stable/c/f95d186255b319c48a365d47b69bd997fecb674e